This invention relates to an improved cutting tool useful for cutting slots in workpieces and is more particularly concerned with an improved cutting tool for gear cutting applications.
It is known in the art of gear cutting to provide for cutting tools which can be easily resharpened by their users by simply regrinding a profile on a cutting end of each tool. The cutting face of such a tool does not require resharpening, and this permits a preservation of the cutting face for metallurgical or other types of treatments which improve cutting and wear characteristics of the tool. In addition, it is known to provide in cutting tools of this type a built-in side rake angle of the cutting face relative to the orientation of such tools in radial slots in cutterheads designed to carry a plurality of tools for gear cutting purposes. Built-in rake angles are disclosed, for example, in U.S. Pat. Nos. 4,060,881 (commonly owned herewith) and 4,137,001. The descriptions of U.S. Pat. No. 4,060,881 are incorporated herein by reference to the extent necessary to provide additional background information regarding the design and usage of certain cutting tools in bevel gear cutting applications. Similar type tools can be used in spur and helical gear cutting applications in which the tools are mounted in a carrier for being brought into engagement with a cylindrical workpiece for forming spur or helical gears.
In the use of tools of the type just described, it has been a practice to utilize three separate designs of tools in a single cutterhead for separately cutting the two sidewalls and the bottom portion of each tooth slot to be formed in a workpiece. Thus, an inside cutting blade is provided to cut one side of the tooth slot, an outside cutting blade is provided to cut an opposite side of the same tooth slot, and bottoming blade is provided for forming the bottom of the tooth slot in the workpiece. With this arrangement, three different designs of cutting blades are required, and three different sharpening set-ups are required for each resharpening of the cutting blades.
It has been found that the function of the bottoming blade can be combined with the two separate side cutting blades in certain completing operations in which a complete tooth slot is formed with a single set-up between tooling and workpiece. This has been accomplished by eliminating the bottoming blade and by providing a cutting edge on each side cutting blade which cuts a portion of the bottom of the tooth slot as well as a portion of one of the sides thereof. Thus, only two types of cutting tools are needed to perform the functions of the three separate tools previously used. In this way a greater number of tools can be provided in a given cutter for working the sides of the tooth slots being formed, and this provides for a faster completing action for the cutter.
However, it is known (as described in U.S. Pat. No. 2,268,326) that when a single cutting tool is required to cut portions of both a side and a bottom of a slot, there is a problem of wing-shaped chips forming along the cutting edge of the tool between the portion of the cutting edge which serves to cut the side of the slot and the portion of the cutting edge which serves to cut the bottom of the slot. These chips tend to compress together in the cutting zone, resulting in a heating up and adhering of the chips to the cutting tool. Chips which do not separate cleanly from the cutting tool can damage the tool, score the surface being cut, and increase drag during the cutting operation.
In order to eliminate these problems so as to produce a better surface finish and a more rapid cutting action, it is a primary purpose of this invention to provide for a chip breaking surface between the two parts of the tool cutting edge that are cutting the two separate parts of a slot in a workpiece. Chip breaking configurations have been used in the past, as shown in U.S. Pat. No. 2,978,792 (commonly owned herewith), for breaking up chips formed in a single part of a tooth slot. Those surfaces were formed on the profile of the cutting end of the tool. Other types of chip breaking surfaces have been provided adjacent to and parallel with the cutting edges of tools. In contrast, the chip breaking surface contemplated by the present invention is formed on the cutting face of the cutting tool and parallel to the axis of the tool, to thereby permit resharpening of the cutting tool profile without disturbing the front face and chip breaking feature of the tool. Additionally, the chip breaking surface of the present invention is positioned at a critical location between the part of the tool that is cutting the bottom of the slot and the part of the tool that is cutting a sidewall portion of the slot. Thus, the cutting tool of the present invention differs both structurally and functionally from what is known to be prior art.
In accordance with a preferred embodiment of the present invention, a gear cutting tool is provided with a chip breaking surface along its cutting face, and the cutting face of the tool is formed at a desired side rake angle for all or part of the length of the tool. Provision of the chip breaking surface on the cutting face provides a cutting edge having a first part for cutting at least a portion of a side of the tooth slot together with a second part for cutting at least a portion of the bottom of the tooth slot. The chipbreaking surface can be formed by grinding one part of the cutting face to a greater depth than its adjoining part to thereby provide offset surfaces for substantially the full length of the cutting face of the tool. This permits resharpening of the profile of the tool without regrinding the cutting face surfaces which have been formed. In addition, the surface which is ground to a greater depth also undercuts the other surface slightly so as to provide a slightly overlapping relationship between the parts of the cutting edge that are forming the separate parts of the tooth slot.
These and other features and advantages of the present invention will become apparent in the more detailed discussion which follows, and in that discussion reference will be made to the accompanying drawings as briefly described below.